Feature: Register a callback to draw the game

In order to have the game drawn We'll register a callback so I do not have to manage it

Scenario: Registering an draw callback
Given a default gameclock
When an draw callback is registered
Then the draw is called regularly

Scenario: Registering a draw callback with a maximum of 50 fps
Given a default gameclock
When maximum fps is 50
Then the draw is called no more than 50 times per second


Scenario: Gameclock needs to use realtime to determine next draw
Given a default gameclock
When maximum fps is given on slow hardware
Then the draw should be scheduled according to realtime



